The present invention relates to a data interpolation method for a decoding apparatus and, more particularly, to a speech signal decoding apparatus using a data interpolation method for a frame data error in transmitting coded data obtained by decomposing a signal (to be transmitted) into frequency regions, i.e., sub-band-coded data, and a method therefor.
Conventionally, in transmitting an input signal, e.g., a speech signal, as coded data having a frame structure, when a transmission path error is detected at the receiving end, data of a frame containing the transmission path error is lost, and the coded data of the frame is replaced with data of the previous frame which was received without an error. With this operation, error data interpolation is performed.
For example, in the technique disclosed in Japanese Patent Laid-Open No. 62-285541, an input speech signal is divided into frames at predetermined time intervals, and a parity bit is added to a parameter representing the characteristic feature of speech data in each frame, thus transmitting the speech signal as data having a frame structure. When a transmission path error in the data of a given frame is detected by a parity bit check at the receiving end, the parameter of the frame is replaced with the parameter of the previous frame, thus performing decoding processing. With this processing, a deterioration in the quality of decoded speed due to a transmission path error is reduced.
The above method can be easily applied to sub-band-coded speech data. If, however, this method is simply applied to sub-band-coded data, the following problem is left unsolved.
In this conventional method, in place of a frame in which a transmission path error has occurred, frame data of the immediately preceding frame is repeatedly decoded. When a speech signal is divided into frequency regions, the low-frequency speech signal component of a frame in which a transmission path error has occurred is rarely replaced with a completely different signal component because low-frequency speech signal components have a high correlation on the time axis. However, the possibility that a high-frequency speech signal component as frame data of a frame in which a transmission path error has occurred is replaced with a different signal component is high because high-frequency speech signal components have a lower time correlation than low-frequency components. For this reason, in the conventional method, the high-frequency component of a frame immediately preceding a frame in which a transmission path error has occurred is also reproduced as decoded data, and the data is detected as high-frequency component noise.